That doesn't take into account the saya (scabbard). In the process of rolling forward, apx. half way through, your saya tip would hit the ground and interupt your roll, could break, could hurt or even impale yourself.

The only thing I can think to say on this is like Nick said: take it out of your obi.

It's a valid question. Anyone have a better/different answer than removing the saya from your obi??

Same difference. By having to keep the weapon sheathed, just push the handle down so that the (covered) blade is pointing up with the handle (mind has gone utterly blank) pointing down. If your head doesn't hit the ground as you roll (which it shouldn't) then the sword will not.